Hello, I have seen this issue before and talked to other mechanics that had this happen to them. The most likely cause is that you cracked the intake. It usually happens near the back corner around cylinder #6. The only other cause would be the intake not being flush against the head. The crack mentioned can be hard to see. You may need to remove the intake to take a closer look at cylinders #1 and #6. Check it out and let me know what you find.